diff --git a/browser/components/extensions/ext-browserAction.js b/browser/components/extensions/ext-browserAction.js
index b24678830c59..275941f3e47e 100644
--- a/browser/components/extensions/ext-browserAction.js
+++ b/browser/components/extensions/ext-browserAction.js
@@ -18,7 +18,7 @@ Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 Cu.import("resource://gre/modules/Task.jsm");
 
 var {
-  EventManager,
+  SingletonEventManager,
   IconDetails,
 } = ExtensionUtils;
 
@@ -446,10 +446,10 @@ extensions.registerSchemaAPI("browserAction", "addon_parent", context => {
   let {extension} = context;
   return {
     browserAction: {
-      onClicked: new EventManager(context, "browserAction.onClicked", fire => {
+      onClicked: new SingletonEventManager(context, "browserAction.onClicked", fire => {
         let listener = () => {
           let tab = TabManager.activeTab;
-          fire(TabManager.convert(extension, tab));
+          fire.async(TabManager.convert(extension, tab));
         };
         BrowserAction.for(extension).on("click", listener);
         return () => {
diff --git a/browser/components/extensions/ext-commands.js b/browser/components/extensions/ext-commands.js
index 416544e860ca..08a5f6af06a2 100644
--- a/browser/components/extensions/ext-commands.js
+++ b/browser/components/extensions/ext-commands.js
@@ -6,7 +6,7 @@ Cu.import("resource://devtools/shared/event-emitter.js");
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 
 var {
-  EventManager,
+  SingletonEventManager,
   PlatformInfo,
 } = ExtensionUtils;
 
@@ -245,9 +245,9 @@ extensions.registerSchemaAPI("commands", "addon_parent", context => {
           });
         }));
       },
-      onCommand: new EventManager(context, "commands.onCommand", fire => {
+      onCommand: new SingletonEventManager(context, "commands.onCommand", fire => {
         let listener = (eventName, commandName) => {
-          fire(commandName);
+          fire.async(commandName);
         };
         commandsMap.get(extension).on("command", listener);
         return () => {
diff --git a/browser/components/extensions/ext-contextMenus.js b/browser/components/extensions/ext-contextMenus.js
index 34a828f13de8..886f10fcf98a 100644
--- a/browser/components/extensions/ext-contextMenus.js
+++ b/browser/components/extensions/ext-contextMenus.js
@@ -8,9 +8,9 @@ Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 var {
-  EventManager,
   ExtensionError,
   IconDetails,
+  SingletonEventManager,
 } = ExtensionUtils;
 
 const ACTION_MENU_TOP_LEVEL_LIMIT = 6;
@@ -625,9 +625,9 @@ extensions.registerSchemaAPI("contextMenus", "addon_parent", context => {
         }
       },
 
-      onClicked: new EventManager(context, "contextMenus.onClicked", fire => {
+      onClicked: new SingletonEventManager(context, "contextMenus.onClicked", fire => {
         let listener = (event, info, tab) => {
-          fire(info, tab);
+          fire.async(info, tab);
         };
 
         extension.on("webext-contextmenu-menuitem-click", listener);
diff --git a/browser/components/extensions/ext-pageAction.js b/browser/components/extensions/ext-pageAction.js
index 4e3299690c12..f4577e808f6e 100644
--- a/browser/components/extensions/ext-pageAction.js
+++ b/browser/components/extensions/ext-pageAction.js
@@ -5,7 +5,7 @@
 Cu.import("resource://gre/modules/Task.jsm");
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 var {
-  EventManager,
+  SingletonEventManager,
   IconDetails,
 } = ExtensionUtils;
 
@@ -244,9 +244,9 @@ extensions.registerSchemaAPI("pageAction", "addon_parent", context => {
   let {extension} = context;
   return {
     pageAction: {
-      onClicked: new EventManager(context, "pageAction.onClicked", fire => {
+      onClicked: new SingletonEventManager(context, "pageAction.onClicked", fire => {
         let listener = (evt, tab) => {
-          fire(TabManager.convert(extension, tab));
+          fire.async(TabManager.convert(extension, tab));
         };
         let pageAction = PageAction.for(extension);
 
diff --git a/browser/components/extensions/ext-tabs.js b/browser/components/extensions/ext-tabs.js
index c835aeb83f84..f6fff15a99cc 100644
--- a/browser/components/extensions/ext-tabs.js
+++ b/browser/components/extensions/ext-tabs.js
@@ -18,7 +18,7 @@ XPCOMUtils.defineLazyModuleGetter(this, "Services",
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 
 var {
-  EventManager,
+  SingletonEventManager,
   ignoreEvent,
 } = ExtensionUtils;
 
@@ -283,12 +283,12 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
         let tab = event.originalTarget;
         let tabId = TabManager.getId(tab);
         let windowId = WindowManager.getId(tab.ownerGlobal);
-        fire({tabId, windowId});
+        fire.async({tabId, windowId});
       }).api(),
 
-      onCreated: new EventManager(context, "tabs.onCreated", fire => {
+      onCreated: new SingletonEventManager(context, "tabs.onCreated", fire => {
         let listener = (eventName, event) => {
-          fire(TabManager.convert(extension, event.tab));
+          fire.async(TabManager.convert(extension, event.tab));
         };
 
         tabListener.on("tab-created", listener);
@@ -307,12 +307,12 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
         let tab = event.originalTarget;
         let tabIds = [TabManager.getId(tab)];
         let windowId = WindowManager.getId(tab.ownerGlobal);
-        fire({tabIds, windowId});
+        fire.async({tabIds, windowId});
       }).api(),
 
-      onAttached: new EventManager(context, "tabs.onAttached", fire => {
+      onAttached: new SingletonEventManager(context, "tabs.onAttached", fire => {
         let listener = (eventName, event) => {
-          fire(event.tabId, {newWindowId: event.newWindowId, newPosition: event.newPosition});
+          fire.async(event.tabId, {newWindowId: event.newWindowId, newPosition: event.newPosition});
         };
 
         tabListener.on("tab-attached", listener);
@@ -321,9 +321,9 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
         };
       }).api(),
 
-      onDetached: new EventManager(context, "tabs.onDetached", fire => {
+      onDetached: new SingletonEventManager(context, "tabs.onDetached", fire => {
         let listener = (eventName, event) => {
-          fire(event.tabId, {oldWindowId: event.oldWindowId, oldPosition: event.oldPosition});
+          fire.async(event.tabId, {oldWindowId: event.oldWindowId, oldPosition: event.oldPosition});
         };
 
         tabListener.on("tab-detached", listener);
@@ -332,9 +332,9 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
         };
       }).api(),
 
-      onRemoved: new EventManager(context, "tabs.onRemoved", fire => {
+      onRemoved: new SingletonEventManager(context, "tabs.onRemoved", fire => {
         let listener = (eventName, event) => {
-          fire(event.tabId, {windowId: event.windowId, isWindowClosing: event.isWindowClosing});
+          fire.async(event.tabId, {windowId: event.windowId, isWindowClosing: event.isWindowClosing});
         };
 
         tabListener.on("tab-removed", listener);
@@ -345,7 +345,7 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
 
       onReplaced: ignoreEvent(context, "tabs.onReplaced"),
 
-      onMoved: new EventManager(context, "tabs.onMoved", fire => {
+      onMoved: new SingletonEventManager(context, "tabs.onMoved", fire => {
         // There are certain circumstances where we need to ignore a move event.
         //
         // Namely, the first time the tab is moved after it's created, we need
@@ -373,7 +373,7 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
             return;
           }
 
-          fire(TabManager.getId(tab), {
+          fire.async(TabManager.getId(tab), {
             windowId: WindowManager.getId(tab.ownerGlobal),
             fromIndex: event.detail,
             toIndex: tab._tPos,
@@ -388,7 +388,7 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
         };
       }).api(),
 
-      onUpdated: new EventManager(context, "tabs.onUpdated", fire => {
+      onUpdated: new SingletonEventManager(context, "tabs.onUpdated", fire => {
         const restricted = ["url", "favIconUrl", "title"];
 
         function sanitize(extension, changeInfo) {
@@ -410,7 +410,7 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
             let tabElem = gBrowser.getTabForBrowser(browser);
 
             let tab = TabManager.convert(extension, tabElem);
-            fire(tab.id, changeInfo, tab);
+            fire.async(tab.id, changeInfo, tab);
           }
         };
 
@@ -447,7 +447,7 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
             for (let prop of needed) {
               changeInfo[prop] = tab[prop];
             }
-            fire(tab.id, changeInfo, tab);
+            fire.async(tab.id, changeInfo, tab);
           }
         };
         let progressListener = {
@@ -1025,7 +1025,7 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
         return Promise.resolve();
       },
 
-      onZoomChange: new EventManager(context, "tabs.onZoomChange", fire => {
+      onZoomChange: new SingletonEventManager(context, "tabs.onZoomChange", fire => {
         let getZoomLevel = browser => {
           let {ZoomManager} = browser.ownerGlobal;
 
@@ -1075,7 +1075,7 @@ extensions.registerSchemaAPI("tabs", "addon_parent", context => {
             zoomLevels.set(browser, newZoomFactor);
 
             let tabId = TabManager.getId(tab);
-            fire({
+            fire.async({
               tabId,
               oldZoomFactor,
               newZoomFactor,
diff --git a/browser/components/extensions/ext-utils.js b/browser/components/extensions/ext-utils.js
index c79eec9d4725..7a010382c378 100644
--- a/browser/components/extensions/ext-utils.js
+++ b/browser/components/extensions/ext-utils.js
@@ -28,8 +28,8 @@ const XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
 
 var {
   DefaultWeakMap,
-  EventManager,
   promiseEvent,
+  SingletonEventManager,
 } = ExtensionUtils;
 
 // This file provides some useful code for the |tabs| and |windows|
@@ -1281,16 +1281,16 @@ global.AllWindowEvents = {
 
 AllWindowEvents.openListener = AllWindowEvents.openListener.bind(AllWindowEvents);
 
-// Subclass of EventManager where we just need to call
+// Subclass of SingletonEventManager where we just need to call
 // add/removeEventListener on each XUL window.
-global.WindowEventManager = function(context, name, event, listener) {
-  EventManager.call(this, context, name, fire => {
-    let listener2 = (...args) => listener(fire, ...args);
-    AllWindowEvents.addListener(event, listener2);
-    return () => {
-      AllWindowEvents.removeListener(event, listener2);
-    };
-  });
+global.WindowEventManager = class extends SingletonEventManager {
+  constructor(context, name, event, listener) {
+    super(context, name, fire => {
+      let listener2 = (...args) => listener(fire, ...args);
+      AllWindowEvents.addListener(event, listener2);
+      return () => {
+        AllWindowEvents.removeListener(event, listener2);
+      };
+    });
+  }
 };
-
-WindowEventManager.prototype = Object.create(EventManager.prototype);
diff --git a/browser/components/extensions/ext-windows.js b/browser/components/extensions/ext-windows.js
index 8f898cb148bf..e76bb8df5f9b 100644
--- a/browser/components/extensions/ext-windows.js
+++ b/browser/components/extensions/ext-windows.js
@@ -12,7 +12,7 @@ XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
 
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 var {
-  EventManager,
+  SingletonEventManager,
   promiseObserved,
 } = ExtensionUtils;
 
@@ -26,15 +26,15 @@ extensions.registerSchemaAPI("windows", "addon_parent", context => {
     windows: {
       onCreated:
       new WindowEventManager(context, "windows.onCreated", "domwindowopened", (fire, window) => {
-        fire(WindowManager.convert(extension, window));
+        fire.async(WindowManager.convert(extension, window));
       }).api(),
 
       onRemoved:
       new WindowEventManager(context, "windows.onRemoved", "domwindowclosed", (fire, window) => {
-        fire(WindowManager.getId(window));
+        fire.async(WindowManager.getId(window));
       }).api(),
 
-      onFocusChanged: new EventManager(context, "windows.onFocusChanged", fire => {
+      onFocusChanged: new SingletonEventManager(context, "windows.onFocusChanged", fire => {
         // Keep track of the last windowId used to fire an onFocusChanged event
         let lastOnFocusChangedWindowId;
 
@@ -45,7 +45,7 @@ extensions.registerSchemaAPI("windows", "addon_parent", context => {
             let window = Services.focus.activeWindow;
             let windowId = window ? WindowManager.getId(window) : WindowManager.WINDOW_ID_NONE;
             if (windowId !== lastOnFocusChangedWindowId) {
-              fire(windowId);
+              fire.async(windowId);
               lastOnFocusChangedWindowId = windowId;
             }
           });
diff --git a/toolkit/components/extensions/ExtensionChild.jsm b/toolkit/components/extensions/ExtensionChild.jsm
index cb30e32598e2..ddccd3c45b50 100644
--- a/toolkit/components/extensions/ExtensionChild.jsm
+++ b/toolkit/components/extensions/ExtensionChild.jsm
@@ -41,7 +41,6 @@ Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 
 const {
   DefaultMap,
-  EventManager,
   SingletonEventManager,
   SpreadArgs,
   defineLazyGetter,
@@ -119,17 +118,17 @@ class Port {
         this.postMessage(json);
       },
 
-      onDisconnect: new EventManager(this.context, "Port.onDisconnect", fire => {
+      onDisconnect: new SingletonEventManager(this.context, "Port.onDisconnect", fire => {
         return this.registerOnDisconnect(error => {
           portError = error && this.context.normalizeError(error);
-          fire.withoutClone(portObj);
+          fire.asyncWithoutClone(portObj);
         });
       }).api(),
 
-      onMessage: new EventManager(this.context, "Port.onMessage", fire => {
+      onMessage: new SingletonEventManager(this.context, "Port.onMessage", fire => {
         return this.registerOnMessage(msg => {
           msg = Cu.cloneInto(msg, this.context.cloneScope);
-          fire.withoutClone(msg, portObj);
+          fire.asyncWithoutClone(msg, portObj);
         });
       }).api(),
 
diff --git a/toolkit/components/extensions/ext-alarms.js b/toolkit/components/extensions/ext-alarms.js
index 2171e7dba6e9..b840d606ef01 100644
--- a/toolkit/components/extensions/ext-alarms.js
+++ b/toolkit/components/extensions/ext-alarms.js
@@ -4,7 +4,7 @@ var {classes: Cc, interfaces: Ci, utils: Cu} = Components;
 
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 var {
-  EventManager,
+  SingletonEventManager,
 } = ExtensionUtils;
 
 // WeakMap[Extension -> Map[name -> Alarm]]
@@ -140,9 +140,9 @@ extensions.registerSchemaAPI("alarms", "addon_parent", context => {
         return Promise.resolve(cleared);
       },
 
-      onAlarm: new EventManager(context, "alarms.onAlarm", fire => {
+      onAlarm: new SingletonEventManager(context, "alarms.onAlarm", fire => {
         let callback = alarm => {
-          fire(alarm.data);
+          fire.sync(alarm.data);
         };
 
         alarmCallbacksMap.get(extension).add(callback);
diff --git a/toolkit/components/extensions/ext-cookies.js b/toolkit/components/extensions/ext-cookies.js
index 05484efb20d3..4e3c41a85ec2 100644
--- a/toolkit/components/extensions/ext-cookies.js
+++ b/toolkit/components/extensions/ext-cookies.js
@@ -9,7 +9,7 @@ XPCOMUtils.defineLazyModuleGetter(this, "ContextualIdentityService",
                                   "resource://gre/modules/ContextualIdentityService.jsm");
 
 var {
-  EventManager,
+  SingletonEventManager,
 } = ExtensionUtils;
 
 var DEFAULT_STORE = "firefox-default";
@@ -438,13 +438,13 @@ extensions.registerSchemaAPI("cookies", "addon_parent", context => {
         return Promise.resolve(result);
       },
 
-      onChanged: new EventManager(context, "cookies.onChanged", fire => {
+      onChanged: new SingletonEventManager(context, "cookies.onChanged", fire => {
         let observer = (subject, topic, data) => {
           let notify = (removed, cookie, cause) => {
             cookie.QueryInterface(Ci.nsICookie2);
 
             if (extension.whiteListedHosts.matchesCookie(cookie)) {
-              fire({removed, cookie: convert({cookie, isPrivate: topic == "private-cookie-changed"}), cause});
+              fire.async({removed, cookie: convert({cookie, isPrivate: topic == "private-cookie-changed"}), cause});
             }
           };
 
diff --git a/toolkit/components/extensions/ext-notifications.js b/toolkit/components/extensions/ext-notifications.js
index 1df96a2ace9a..df2de578083c 100644
--- a/toolkit/components/extensions/ext-notifications.js
+++ b/toolkit/components/extensions/ext-notifications.js
@@ -8,7 +8,7 @@ XPCOMUtils.defineLazyModuleGetter(this, "EventEmitter",
                                   "resource://devtools/shared/event-emitter.js");
 
 var {
-  EventManager,
+  SingletonEventManager,
   ignoreEvent,
 } = ExtensionUtils;
 
@@ -131,10 +131,10 @@ extensions.registerSchemaAPI("notifications", "addon_parent", context => {
         return Promise.resolve(result);
       },
 
-      onClosed: new EventManager(context, "notifications.onClosed", fire => {
+      onClosed: new SingletonEventManager(context, "notifications.onClosed", fire => {
         let listener = (event, notificationId) => {
           // FIXME: Support the byUser argument.
-          fire(notificationId, true);
+          fire.async(notificationId, true);
         };
 
         notificationsMap.get(extension).on("closed", listener);
@@ -143,9 +143,9 @@ extensions.registerSchemaAPI("notifications", "addon_parent", context => {
         };
       }).api(),
 
-      onClicked: new EventManager(context, "notifications.onClicked", fire => {
+      onClicked: new SingletonEventManager(context, "notifications.onClicked", fire => {
         let listener = (event, notificationId) => {
-          fire(notificationId, true);
+          fire.async(notificationId, true);
         };
 
         notificationsMap.get(extension).on("clicked", listener);
diff --git a/toolkit/components/extensions/ext-storage.js b/toolkit/components/extensions/ext-storage.js
index 2f17f82d5417..0155ad6948f8 100644
--- a/toolkit/components/extensions/ext-storage.js
+++ b/toolkit/components/extensions/ext-storage.js
@@ -11,8 +11,8 @@ XPCOMUtils.defineLazyModuleGetter(this, "AddonManagerPrivate",
 
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 var {
-  EventManager,
   ExtensionError,
+  SingletonEventManager,
 } = ExtensionUtils;
 
 function enforceNoTemporaryAddon(extensionId) {
@@ -63,12 +63,12 @@ function storageApiFactory(context) {
         },
       },
 
-      onChanged: new EventManager(context, "storage.onChanged", fire => {
+      onChanged: new SingletonEventManager(context, "storage.onChanged", fire => {
         let listenerLocal = changes => {
-          fire(changes, "local");
+          fire.async(changes, "local");
         };
         let listenerSync = changes => {
-          fire(changes, "sync");
+          fire.async(changes, "sync");
         };
 
         ExtensionStorage.addOnChangedListener(extension.id, listenerLocal);